This July 24, 2012 photo provided by the U.S. Air Force shows a B-1 bomber rumbling down the flightline at Ellsworth Air Force Base, S.D., as part of a training mission. On Tuesday, March 24, 2015, the Federal Aviation Administration gave final approval for a plan to establish an enormous bomber training area over the northern Plains that advocates say will improve military training and save money. The plan would expand the Powder River Training Complex over the Dakotas, Montana and Wyoming. The move quadruples the training airspace, making it the largest over the continental United States. (AP Photo/U.S. Air Force, Airman 1st Class Zachary Hada)

FILE - In this Aug. 9, 2007, file photo, B-52 bombers taxi to the runway at Minot Air Force Base in Minot, N.D. On Tuesday, March 24, 2015, the Federal Aviation Administration gave final approval for a plan to establish an enormous bomber training area over the northern Plains that advocates say will improve military training and save money. The plan would expand the Powder River Training Complex over the Dakotas, Montana and Wyoming. The move quadruples the training airspace, making it the largest over the continental United States. (AP Photo/The Minot Daily News, Eloise Ogden, File)

PIERRE, South Dakota — A proposal to establish an enormous bomber training area over the northern Plains that advocates say will improve military training and save money got final approval Tuesday despite concerns about loud, low-flying aircraft disrupting civilian flights and damaging rural economies.

The Federal Aviation Administration approved a plan to expand the Powder River Training Complex over the Dakotas, Montana and Wyoming. The move roughly quadruples the training airspace to span across nearly 35,000 square miles, making it the largest over the continental U.S.

The airspace would be used by B-1 bombers from Ellsworth Air Force Base in South Dakota and B-52 bombers from Minot Air Force Base in North Dakota. The U.S. Air Force estimates that the expanded training airspace could save Ellsworth up to $23 million a year in fuel costs by reducing the number of training flights to states such as Utah and Nevada.

"This is great news, and it does mark the final step in a very long process," South Dakota U.S. Sen. John Thune, who has been pushing for the expansion since 2006, told The Associated Press. "I think this creates the kind of opportunity for Ellsworth to really be a jewel when it comes to all the different installations that we have around the country."

The Air Force approved the expansion in January, which kicked the proposal over to the FAA for review.

Col. Kevin Kennedy, 28th Bomb Wing commander, said in a statement that the expansion will "greatly improve the training opportunities and readiness of Ellsworth and Minot aircrews."

Training exercises in the expanded airspace will likely be underway by the end of the year.

Thune said the expansion could shield Ellsworth from being shut down under Base Realignment and Closure, a federal cost-cutting program. Ellsworth is a significant economic driver for the Rapid City area and was under consideration for closure in 2005.

But elected leaders in Montana and state aviation officials have said the bombers would disrupt rural communities and scare livestock as they roar overhead on maneuvers, dropping flares and chaff, or fiber clusters intended to disturb radar waves.

"I'm extremely disappointed the FAA is greenlighting this expansion in the face of real concerns and opposition on the ground," Montana U.S. Sen. Jon Tester said in a statement. "I will hold the Air Force and the FAA accountable as this expansion moves forward to ensure the training complex doesn't negatively impact general aviation, agriculture production or energy development."

The Air Force acknowledged in a study released in November that the low-altitude flights and loud sonic booms could startle residents and livestock, including those living on four Native American reservations in the region.

Under the Air Force plan, any given location across the training area could experience up to nine low-altitude overflights annually. Supersonic flights would be limited to 10 days a year during large-scale exercises involving roughly 20 aircraft.

As many as 88 civilian flights a day could be delayed when the large-scale exercises are conducted, the Air Force wrote in January. Capt. Christopher Diaz, 28th Bomb Wing Chief of Public Affairs, said in an email that it's possibly but "not likely" that training would affect that many flights.

Roger Meggers, who manages eastern Montana's Baker Municipal Airport, was in Washington on Tuesday meeting with lawmakers about the expansion. Meggers said the expanded airspace would cause significant delays at his small airport, and he said military aircraft traveling at high speeds are a serious safety concern for other aviators.

"We're disappointed and feel that the aircraft and public safety is at risk with the way it's going forward," he said. "It's definitely a plus for South Dakota at the expense of Montana."

Thune said he intended to work with the Air Force and others "to make sure the local concerns continue to be taken into account."